1. Field of the Invention
The present invention relates to the flexible transmission of multilayer media data, and more particularly, to a method and apparatus of transmitting and receiving a flexible MMT asset in a hybrid delivery-based MMT (MPEG Media Transport) service.
2. Discussion of the Related Art
Since the standardization of MPEG-2, new standards for video encoding standard (or an audio encoding standard) have been steadily developed into MPEG-4, H.264/AVC, and Scalable Video Coding (SVC) in the last 10 years. Furthermore, each of the new standards has made a new market and widened the application scope of the MPEG standard. Transmission technology, such as MPEG-2 Transport System (TS), however, has been widely used in digital broadcasting and mobile broadcasting (T-DMB, DVB-H, etc.) in the market during the past 20 years without change. The transmission technology has been widely utilized even in multimedia transmission over the Internet, i.e. IPTV service, that had not been considered when the MPEG-2 TS standard was established.
However, a multimedia transmission environment when the MPEG-2 TS was developed and a current multimedia transmission environment have been significantly varied. For example, the MPEG-2 TS standard was developed by considering the transmission of multimedia data over an ATM network, but it has become difficult to find use cases where the MPEG-2 TS standard is used for this purpose. Furthermore, the MPEG-2 TS standard includes factors that are not efficient for recent multimedia transmission over the Internet because requirements, such as requirements for multimedia transmission via the Internet, were not taken into consideration when the MPEG-2 TS standard was developed. Accordingly, in MPEG, the establishment of an MPEG Multimedia Transport Layer (MMT), that is, a new multimedia transmission standard which is suitable for a varying multimedia environment and into which multimedia service through the Internet has been taken into consideration, is recognized as a very important problem.
As described above, an important reason why MMT standardization is in progress lies in that the MPEG2-TS standard completed 20 years ago has not been optimized for the recent IPTV broadcasting service, Internet environment, etc. For this reason, in MPEG, the MMT has been standardized as a new transmission technology standard according to an urgent need for a multimedia transmission international standard that is optimized in a multimedia transmission environment in a variety of recent heterogeneous networks. The conventional MPTEG 2 TS standard alone cannot provide sufficient support for a variety of application examples for hybrid delivery (or transmission) over a broadcast network and a broadband network.
Hybrid delivery-based MMT service enables the delivery of multiple media data to a client device from different servers via multiple paths (e.g., other channels or networks). In this case, the client device has to be able to service a plurality of received media streams while keeping them in synchronization in an integrated fashion.
However, according to the CMMT SoCD (Study of Committee Draft) which is currently in progress, every layer of multilayer media data must be included in a single MPU (Media Processing Unit). As an MMT asset is a collection of one or more MPUs, every layer belongs to a single MMT asset. In this case, every layer has a single ADC (Asset Delivery Characteristic). Accordingly, the current MMT SoCD cannot provide sufficient support for hybrid delivery by which individual layers of the multilayer are assigned different delivery characteristics and transmitted via multiple paths.